Othovisc is a sterile solution of 1.5% sodium hyaluronate in physiologic saline. This material occurs naturally in joint fluid, where it reduces joint friction, and is largely responsible for the viscosity of normal synovial fluid. A similar solution of hyaluronate has been used in the United States in the eye, and in many other countries hyaluronate solutions are used safely, as intra-articular injections, to treat arthritis. We have recently conducted a randomized, double blind controlled trial to assess the safety and effectiveness of a series of three weekly intra articular injections of Orthovisc in providing pain relief for osteoarthritis of the knee. No serious adverse events have occurred in this trial, which is nearing completion. Now, 80 or the 220 subjects enrolled in that study at 10 investigational sites will be eligible to enroll in a new open label trial. In this study intended to assess the safety and effectiveness of a second series of injections, each subject will be enrolled at this center. Therapeutic efficacy will be assessed in terms of patient and investigator global assessment, and knee pain on standing and walking. The standardized WOMAC questionnaire used in the Anika I trial will be used to evaluate patient function. A physical examination of the knee and synovial fluid analysis, and observation for adverse effects will be performed to assess treatment safety.